1. Field of the Invention:
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and method for performing call setup by a relay of a Mobile Station (MS) being at a cell edge to provide a communication service to an MS being out of a cell area in a wireless communication system.
2. Description of the Related Art:
Wireless communication systems support an emergency call service to quickly address an emergency situation such as an accident, etc. Types of the emergency call service may be described as follows.
A first type is using a predetermined key to a wireless communication terminal, or pressing a combination of keys, thus establishing a quick emergency call.
A second type is enabling a quick connection to a predetermined contact using a menu of a wireless communication terminal.
FIGS. 1A, 1B and 1C illustrate an emergency call using Peer-to-Peer (P2P) communication in a wireless communication system according to a conventional art.
Referring to FIG. 1A, a Mobile Station (MS) 102 is within a cell area 100 enabling signal reception from a Base Station (BS) 101 and thus, communicates with the BS 101 through radio resources (e.g., frequencies) (104). An MS 103 is out of the cell area 100 and disables signal reception from the BS 101 and thus, is not able to communicate with the BS 101 (105). If it is an UpLink (UL) transmission duration, the MS 102 is allocated UL resources and performs UL transmission using a power level receivable by the BS 101 (106). At this time, the MS 102 can forward a signal even to the neighboring MS 103 that is out of the cell area 100 (107) as shown in FIG. 1B. Thus, when the MS 103 sends an emergency call request, etc., out of the cell area 100 (109), the MS 103 can perform an emergency call with the BS 101 (108) through the neighboring MS 102 as shown in FIG. 1C because the MS 103 is not able to directly communicate with the BS 101.
In order to provide an emergency call service to the MS 103 being out of the cell area 100 through a relay of the MS 102 being at a cell edge portion, synchronization procedures between the two MSs 102 and 103 have to be essentially performed. In the conventional art, in order to achieve synchronization between the MS 103 sending an emergency call request and the MS 102 relaying the emergency call request up to the BS 101, the MS 103 has to continuously transmit an emergency call request message until receiving an acknowledgement message to the emergency call request using reserved resources. Because of this, the MS 103 increasingly consumes power until receiving the acknowledgement message responsive to the emergency call request.
An emergency call seldom occurs. Also, the MS 102 receiving a communication service from the BS 101 is not able to recognize when an emergency call is generated. If resources to be used in the event of an emergency call are always reserved through allocation of a specific time-frequency resource among wireless communication resources but is not used in the BS 101, frequency efficiency is deteriorated. If an MS transmits a packet for an emergency call request using any time-frequency resource, the MS may cause interference on other MSs within a corresponding service coverage area.
As described above, in the conventional art, if an MS is out of a service coverage area and encounters an emergency situation, MSs being at a cell edge portion are difficult to recognize when an emergency call is generated upon an emergency call request. Furthermore, operating time-frequency resources in a manner in which they are always reserved for such an emergency call results in a great disadvantage in efficiency.